The principal objective of this proposal is to characterize a conditioned medium factor which dramatically stimulates the regeneration of nerve fibers from isolated nerve cells in culture. Interest in this factor arises from its potential use in promoting the regeneration of injured nerves in living animals. Use of this factor has already allowed us to induce sprouting of nerve fibers in vitro which is exceptional in its rapidity and synchrony and in the very high percentage of responding neurons. I am proposing to determine the range of nerve cell types which respond to this factor, the types of cell which produce it, to further purify and chemically characterize the factor, and to assess its ability to promote regeneration when applied to injured nerves in animals which are a good model of human peripheral nerve injuries.